CN102694054B - Light receiving element, optical pickup apparatus and Optical Receivers - Google Patents

Abstract

The invention discloses a kind of light receiving element, optical pickup apparatus and Optical Receivers, wherein said light receiving element, comprising: core, is configured to transmitting signal light; First semiconductor layer, has the first conduction type, and the first direction that described first semiconductor layer is configured to extend along described core is from flashlight described in described core accepts; Absorbed layer, is configured to absorb the described flashlight received by described first semiconductor layer; And second semiconductor layer, there is second conduction type contrary with described first conduction type.

Description

Light receiving element, light receiving device and light receiving module

technical field

Embodiments discussed in the present invention relate to a light receiving element, a light receiving device, and a light receiving module.

Background technique

FIG. 1 is a perspective view showing a main part of a light receiving element 100 as an example of a light receiving element. FIG. 2 is a cross-sectional view of the light receiving element 100 taken along the dotted line II-II in FIG. 1 .

The light receiving element 100 shown in FIGS. 1 and 2 includes a photo-detector unit 101 provided over a substrate 114 , and a waveguide unit 111 provided over the same substrate 114 . The waveguide unit 111 includes a core 112 having a rib-like shape. The signal light propagates inside the protrusion 113 of the core 112 and enters the photodetector unit 101 .

The photodetector unit 101 has a structure in which a core 112, an n-type semiconductor layer 102, an i-type absorbing layer 103, a p-type upper cladding layer 104, and a p-type contact layer are stacked from the substrate 114 side 105. Photodetector unit 101 has a mesa structure including p-type contact layer 105 , p-type upper cladding layer 104 , and i-type absorption layer 103 . The core 112 exists in both the photodetector unit 101 and the waveguide unit 111 .

As shown in FIG. 2 , in the light receiving element 100 , signal light propagates under the protrusion 113 of the core 112 in the waveguide unit 111 , and enters the core 112 in the photodetector unit 101 . Part of the incident signal light penetrates into the n-type semiconductor layer 102 . As the signal light further propagates in the photodetector unit 101 , the signal light propagates to the i-type absorbing layer 103 and is absorbed in the i-type absorbing layer 103 .

The n-type semiconductor layer 102, the i-type absorption layer 103, and the p-type upper cladding layer 104 form a PIN-type photodiode (hereinafter referred to as PD). A p-side electrode and an n-side electrode (not shown) are connected to the p-type contact layer 105 and the n-type semiconductor layer 102, respectively. By applying a predetermined voltage between the p-side electrode and the n-side electrode, with the p-side electrode at a negative potential and the n-side electrode at a positive potential, via the p-type upper cladding layer 104 and the n-type semiconductor Layer 102 detects photocarriers (holes and electrons) generated by light absorption in i-type absorber layer 103 . Thus, the photodetector unit 101 detects signal light as an electrical signal (photocarrier current), and outputs a detection signal (photocarrier current) corresponding to the intensity of the signal light.

FIG. 3 shows a main part of a light receiving element 300 as another example of a light receiving element. FIG. 4 is a cross-sectional view of the light receiving element 300 taken along the dotted line IV-IV in FIG. 3 .

The light receiving element 300 shown in FIGS. 3 and 4 has a structure different from that of the light receiving element shown in FIGS. 1 and 2 . The light receiving element 300 includes a photodetector unit 301 provided over a substrate 314 , and a waveguide unit 311 provided over the same substrate 314 .

The waveguide unit 311 has a structure in which an n-type lower cladding layer 302, a core 312, and an upper cladding layer 313 are stacked from the substrate 314 side. The waveguide unit 311 has a mesa structure including an upper clad layer 313 and a core 312 . The signal light propagates in the core 312 and enters the photodetector unit 301 .

The photodetector unit 301 has a structure in which an n-type lower cladding layer 302, an i-type absorbing layer 303, a p-type upper cladding layer 304, and a p-type contact layer 305 are stacked from the substrate 314 side. . The photodetector unit 301 has a mesa structure including a p-type contact layer 305 , a p-type upper cladding layer 304 , and an i-type absorbing layer 303 .

Both the core 312 and the i-type absorbing layer 303 are formed on the n-type lower cladding layer 302 shared by the photodetector unit 301 and the waveguide unit 311 . The core 312 is attached to the side surface of the i-type absorber layer 303 .

As shown in FIG. 4 , in the light receiving element 300 , signal light propagates in the core 312 in the waveguide unit 311 and directly enters the i-type absorbing layer 303 in the photodetector unit 301 . The incident signal light is absorbed into a region near the end face of the i-type absorbing layer 303 from which the signal light enters.

The n-type lower cladding layer 302, the i-type absorber layer 303 and the p-type upper cladding layer 304 form a PIN-type photodiode. The p-side electrode and the n-side electrode are connected to the p-type contact layer 305 and the n-type lower cladding layer 302, respectively. By applying a predetermined voltage between the p-side electrode and the n-side electrode, with the p-side electrode at a negative potential and the n-side electrode at a positive potential, via the p-type upper cladding layer 304 and the lower cladding layer 302 detects photogenerated carriers (holes and electrons) generated by light absorption in the i-type absorber layer 303 . Thus, the photodetector unit 301 detects signal light as an electrical signal (photocarrier current), and outputs a detection signal (photocarrier current) corresponding to the intensity of the signal light.

In Japanese Laid-Open Patent Publication No. 2003-163363 and Andreas Beling et al. published on February 1, 2009 in Volume 27, No. 3, No. 343-355 of "J. Lightwave Technology" (J.Lightwave Tech.) In this page, examples of two light receiving elements 100 and 300 as shown in FIGS. 1 to 4 are discussed.

FIG. 5 shows an example of simulated concentration distributions of photogenerated carriers generated in photodetector units 101 and 301 . The vertical axis represents the concentration of photogenerated carriers when normalized based on a predetermined value. The horizontal axis represents the position within the PD in each of the photodetector units 101 and 301 . In this specification, the term "position within the PD" refers to a position within the PD along the extending direction of the corresponding core (ie, the direction in which the signal light travels), and means the position within the PD included in the photodetector unit. Reference is made to the position of the end at which signal light enters the photodetector unit. In addition, the term "PD length" refers to the length of the PD in the photodetector unit along the direction in which the corresponding core extends (ie, the direction in which the signal light travels), and means that the PD in the photodetector unit refers to the direction in which the signal light enters the photoelectric sensor. The length of the end face of the detector unit.

In FIG. 5, the curve shown by (a) represents the photogenerated carrier concentration distribution in the photodetector unit 101 shown in FIG. 1 and FIG. 2, and the curve shown by (b) represents the and the photogenerated carrier concentration distribution in the photodetector unit 301 shown in FIG. 4 .

In the photodetector unit 101 of the light receiving element 100, the signal light penetrates into the i-type absorbing layer 103 after propagating through the core 112 and the n-type semiconductor layer 102 in the photodetector unit 101 for a predetermined distance, thus absorption occurs . Therefore, as is apparent from the distribution curve (a) in FIG. 5 , the peak of the photogenerated carrier concentration distribution occurs at a position spaced a predetermined distance from the end face of the photodetector unit 101 from which the signal light enters. Furthermore, the overall concentration distribution also extends to a position further away from the photodetector unit 101 , so that the distribution as a whole has a large extension.

Therefore, in the photodetector unit 101, the PD length of the photodetector unit 101 is set to a sufficient length for obtaining sufficient absorption efficiency. However, making the PD length of the photodetector unit 101 longer increases the size of the capacitor including the n-type semiconductor layer 102, the i-type absorbing layer 103, and the p-type upper cladding layer 104, resulting in a larger size of the photodetector unit 101. Capacitance increases. Thus, the cutoff frequency derived from the CR time constant becomes lower in the transmission path between the light receiving element 100 and the subsequent electronic circuit. Therefore, in the subsequent electronic circuit for receiving the electric signal output from the light receiving element 100, the level of the input signal is attenuated at high frequencies, making it difficult to properly process the input signal also at high frequencies.

As a result, with the structure of the light receiving element 100 shown in FIGS. 1 and 2 , it is difficult to supply a detection signal with a sufficient signal level to a subsequent electronic circuit while ensuring high light absorption efficiency.

On the other hand, in the photodetector unit 301 of the light receiving element 300 , the signal light that has propagated through the core 312 directly enters the i-type absorption layer 303 . Therefore, large absorption occurs near the end face of the photodetector unit 301 . Thus, as is apparent from the distribution curve (b) in FIG. 5 , photogenerated carriers are generated and their concentration becomes high in a narrow range near the end face of the photodetector unit 301 from which signal light enters.

Therefore, in the photodetector unit 301, high light absorption efficiency can be obtained even if the PD length is short. However, since the rising edge of the photogenerated carrier concentration distribution is very large in the vicinity of the end face of the photodetector unit 301 in the case of high-intensity light input in which the intensity of the input signal light is high, the end face of the photodetector unit 301 The concentration of locally generated photo-generated carriers in the vicinity becomes very high. As a result, in the photodetector unit 301, in the direction opposite to the electric field generated by the above-mentioned voltage applied between the p-side electrode and the n-side electrode, too many locally generated photocarriers A large magnetic field is generated between the p-type upper cladding layer 304 and the n-type lower cladding layer 302 . The electric field generated by the excess locally generated photo-generated carriers serves to counteract the electric field generated by the above-mentioned voltage applied between the p-side electrode and the n-side electrode. This makes it difficult for the photodetector unit 301 to properly detect photogenerated carriers generated by light absorption in the i-type absorber layer 303 via the p-type upper cladding layer 304 and the n-type lower cladding layer 302 (holes and electrons). Therefore, the high-frequency characteristics of the high-intensity signal light deteriorate.

As a result, with the structure of the light receiving element 300 as shown in FIGS. 3 and 4 , it is difficult to perform an output operation suitable for high-intensity light input.

Contents of the invention

Therefore, an object of one aspect of the embodiment is to provide a light receiving element in which a detection signal having a sufficient signal level can be supplied at a high frequency to subsequent an electronic circuit; and providing a light receiving element that performs an output operation suitable for high-intensity light input in which the intensity of input signal light is high.

According to an aspect of the present invention, a light receiving element includes: a core configured to propagate signal light; a first semiconductor layer having a first conductivity type configured to move from the a core receiving the signal light, the core extending in the first direction; an absorbing layer configured to absorb the signal light received by the first semiconductor layer; and a second semiconductor layer having a A second conductivity type opposite to the first conductivity type.

Description of drawings

FIG. 1 is a perspective view showing an example of a related art light receiving element;

FIG. 2 is a cross-sectional view of a light-receiving element along the dotted line II-II in FIG. 1 of the related art;

3 is a perspective view showing another example of a related art light receiving element;

4 is a cross-sectional view of a related art light receiving element along the dotted line IV-IV in FIG. 3;

FIG. 5 shows an example of a simulated light absorption distribution in a related art photodetector unit;

6 is a perspective view showing an example of the structure of the light receiving element according to the first embodiment;

Fig. 7 is a cross-sectional view of the light receiving element along the dotted line VII-VII in Fig. 6;

8 shows an example of a simulated concentration distribution of photogenerated carriers generated in a photodetector cell of a light receiving element;

FIG. 9 shows an example of simulated quantum efficiency in a photodetector unit of a light receiving element;

10 is a perspective view showing an example of the structure of a light receiving element;

Fig. 11 is a sectional view of the light receiving element along the dotted line XI-XI in Fig. 10;

12A and 12B are cross-sectional views of the light-receiving element along dotted lines XIIA-XIIA and XIIB-XIIB in FIG. 10, respectively;

13A and 13B show an example (first part) of the manufacturing process of the light receiving element shown in FIGS. 10 to 12B;

14A and 14B show an example (second part) of the manufacturing process of the light receiving element shown in FIGS. 10 to 12B;

15A and 15B show an example (third part) of the manufacturing process of the light receiving element shown in FIGS. 10 to 12B;

16A and 16B show an example (fourth part) of the manufacturing process of the light receiving element shown in FIGS. 10 to 12B;

17A and 17B show an example of the manufacturing process of the light receiving element shown in FIGS. 10 to 12B (part five);

18 is a sectional view showing an example of the structure of a light receiving element according to a second embodiment;

19 is a cross-sectional view showing an example of the structure of a light receiving element according to a third embodiment;

FIG. 20 shows an example of a simulated concentration distribution of photogenerated carriers generated in a photodetector cell of a light receiving element;

21 is a sectional view showing an example of the structure of a light receiving element according to a fourth embodiment;

22 is a plan view showing an example of the configuration of a light receiving device according to a fifth embodiment;

Fig. 23 is a plan view showing one example of the configuration of a light receiving module according to a sixth embodiment.

Detailed ways

In the following, a number of embodiments are described.

Example

[1. First embodiment]

[1-1 Structure of Light Receiving Element 600 ]

FIG. 6 is a perspective view showing an example of the structure of a light receiving element 600 according to the first embodiment. FIG. 6 shows only the main part of the light receiving element 600 . FIG. 7 is a cross-sectional view of the light receiving element 600 along the dotted line VII-VII in FIG. 6 . FIG. 7 shows the vicinity of the boundary region between the photodetector unit 601 and the waveguide unit 611 .

In the specification, with respect to the substrate surface side of the structure on which the light receiving element is formed, a direction pointing away from the substrate surface is referred to as "upper", "top", "above", "on" or "above", and directed toward The direction toward the surface of the substrate is referred to as "lower", "bottom", "beneath" or "under".

As shown in FIGS. 6 and 7 , the light receiving element 600 includes a photodetector unit 601 provided over a substrate 614 and a waveguide unit 611 provided over the same substrate 614 .

The waveguide unit 611 has a structure in which a core 612 and an upper cladding layer 613 are laminated from the substrate 614 side. The material of each layer of the stacked structure is, for example, semiconductor. The waveguide unit 611 has a mesa structure including an upper clad layer 613 and a core 612 . The signal light propagates in the core 612 and enters the photodetector unit 601 .

The photodetector unit 601 has a structure in which an n-type semiconductor layer 602, an i-type absorption layer 603, a p-type upper cladding layer 604, and a p-type contact layer 605 are stacked from the substrate 614 side. The material of each layer of the stacked structure is, for example, semiconductor. The photodetector unit 601 has a mesa structure including a p-type contact layer 605 , a p-type upper cladding layer 604 , an i-type absorbing layer 603 and part of an n-type semiconductor layer 602 . The n-type semiconductor layer 602, the i-type absorber layer 603 and the p-type upper cladding layer 604 form a PIN-type photodiode.

As shown in FIG. 7, in light receiving element 600, core 612 is connected to the side surface of n-type semiconductor layer 602, and core 612 and n-type semiconductor layer 602 are connected adjacent to each other along the direction in which core 612 extends. The core 612 is formed such that its top surface is set higher than the bottom surface of the n-type semiconductor layer 602 (set farther from the substrate 614), and its bottom surface is set lower than the top surface of the n-type semiconductor layer 602 ( set closer to the substrate 614).

The n-type semiconductor layer 602 is formed such that its refractive index is higher than that of the core 612 and lower than that of the i-type absorbing layer 603 . That is, the n-type semiconductor layer 602 is formed such that its bandgap wavelength is longer than that of the core 612 and shorter than that of the i-type absorbing layer 603 . The n-type semiconductor layer 602 is formed to have a composition such that the absorption coefficient for signal light is sufficiently small.

As shown in FIG. 7 , in the light receiving element 600 , signal light propagates in the core 612 in the waveguide unit 611 and enters the n-type semiconductor layer 602 in the photodetector unit 601 . The n-type semiconductor layer 602 receives signal light from the core 612 along the direction in which the core 612 extends. Since the refractive index of the n-type semiconductor layer 602 is set higher than that of the core 612, the loss of signal light when entering the n-type semiconductor layer 602 from the core 612 can be reduced. Part of the incident signal light permeates from the n-type semiconductor layer 602 into the i-type absorbing layer 603 and is absorbed in the i-type absorbing layer 603 .

A p-side electrode and an n-side electrode (not shown) are connected to the p-type contact layer 605 and the n-type semiconductor layer 602, respectively. By applying a predetermined voltage between the p-side electrode and the n-side electrode, with the p-side electrode at a negative potential and the n-side electrode at a positive potential, via the p-type upper clad layer 604 and the n-type semiconductor Layer 602 detects photogenerated carriers (holes and electrons) generated by light absorption in i-type absorber layer 603 . Thus, the photodetector unit 601 detects signal light as an electrical signal, and generates a detection signal as an electrical signal (photocarrier current). The photodetector unit 601 outputs a detection signal (photogenerated carrier current) corresponding to the intensity of signal light to a subsequent electronic circuit.

In the photodetector unit 601, unlike in the photodetector unit 101 of the light receiving element 100 shown in FIG. 1 and FIG. 602 , and the absorption of signal light occurs in the i-type absorbing layer 603 . Therefore, in the photodetector unit 601, as soon as the signal light enters the n-type semiconductor layer 602, the signal light permeates into the i-type absorbing layer 603, thereby starting to absorb the signal light immediately after the signal light enters. Therefore, in the photodetector unit 601 , the PD length can be made shorter than the PD length of the photodetector unit 101 while ensuring sufficient light absorption efficiency.

Since the PD length in the photodetector unit 601 can be shortened, the size of the capacitor including the n-type semiconductor layer 602, the i-type absorbing layer 603, and the p-type upper cladding layer 604 can be made smaller. Therefore, the capacitance of the photodetector unit 601 can be lowered, and thus the cutoff frequency deduced from the CR time constant becomes higher in the transmission path between the light receiving element 600 and the subsequent electronic circuit. Therefore, the light receiving element 600 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency, thereby enabling the subsequent electronic circuit to process an input signal also at a high frequency.

Furthermore, in the light receiving element 600, unlike in the photodetector unit 301 of the light receiving element 300 shown in FIGS. The semiconductor layer 602, and then its components that penetrate into the i-type absorbing layer 603 are absorbed. Thus, in photodetector cell 601 , the overall concentration of generated photogenerated carriers is a flat, slightly sloped profile compared to that in photodetector cell 301 .

Therefore, in the photodetector unit 601, even in the case of high-intensity light input in which the intensity of input signal light is high, an excessive increase in local photogenerated carrier concentration can be reduced. Thus, in the photodetector unit 601, it is possible to reduce degradation of high-frequency characteristics of a high-intensity signal due to the influence of an electric field generated by photogenerated carriers (holes and electrons). Therefore, in the light receiving element 600, an output operation suitable for high-intensity light input can be performed.

As has been described above, in the light receiving element 600 , while improving the efficiency of light absorption in the photodetector unit 601 , it is also possible to supply a detection signal with a sufficient signal level at a high frequency to a subsequent electronic circuit. In addition, the light receiving element 600 can perform an output operation suitable for a high-intensity light input in which the intensity of the input signal light is high.

[1.2 Photogenerated carrier concentration distribution in the photodetector unit 601]

FIG. 8 shows one example of a simulated concentration distribution of photogenerated carriers generated in the photodetector unit 601 of the light receiving element 600 . The vertical axis represents the concentration of photogenerated carriers when normalized based on a predetermined value. The horizontal axis represents the position within the PD in the photodetector unit 601 .

In FIG. 8 , the curve shown by (c) represents the photogenerated carrier concentration distribution in the photodetector unit 601 of the light receiving element 600 shown in FIGS. 6 and 7 . In FIG. 8, for comparison, the photogenerated carrier concentration distribution in the photodetector unit 101 of the light receiving element 100 shown in FIGS. 1 and 2 is represented as a curve (a), and as shown in FIGS. 3 and 4 The photogenerated carrier concentration distribution in the photodetector unit 301 of the light receiving element 300 shown is represented by a curve (b). The distribution curves (a) and (b) in FIGS. 8 and 9 are the same as the distribution curves (a) and (b) in FIG. 5 .

As represented by the distribution curve (c), in the case of the light receiving element 600, compared with the photoconnecting element 100 (distribution curve (a)), the peak value of the photogenerated carrier concentration distribution is located at a distance of 601 from the photodetector unit 601. close to the end. Therefore, the overall photogenerated carrier concentration distribution is also shifted to the side closer to the end face of the photodetector unit 601 , and the extension of the distribution as a whole is also small.

Therefore, in the light receiving element 600 , the PD length of the photodetector unit 601 can be made shorter than the PD length of the photodetector unit 101 in the light receiving element 100 while ensuring sufficient light absorption efficiency. For example, estimated from the shift amount of the peak position, about 2/3 of the PD length of the photodetector unit 101 is sufficient as the PD length of the photodetector unit 601 in order to obtain the same light absorption coefficient.

Since the PD length can be shortened, the capacitance of the photodetector unit 601 also becomes smaller than that of the photodetector unit 101 . Thus, the light receiving element 600 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency, thereby enabling the subsequent electronic circuit to process an input signal at a high frequency as well.

In addition, as represented by the distribution curve (c), in the light receiving element 600, the peak value of the photogenerated carrier concentration distribution is higher than that of the photogenerated carrier concentration distribution (distribution curve (b)) in the light receiving element 300. The peak is low enough. In the light receiving element 600 , the concentration value at the peak position of the photogenerated carrier concentration distribution is sufficiently smaller than the maximum value of the concentration in the case of the light receiving element 300 (distribution curve (b)). In addition, the density distribution as a whole is a flat, slightly inclined distribution compared with the density distribution of the light receiving element 300 (distribution curve (b)).

Therefore, even in the case of high-intensity light input in which the intensity of input signal light is high, an excessive increase in local photogenerated carrier concentration can be reduced. Thus, in the light receiving element 600, degradation of high-frequency characteristics of high-intensity signal light can be reduced.

As described above, in the light receiving element 600 , while improving the light absorption efficiency in the photodetector unit 601 , it is also possible to supply a detection signal having a sufficient signal level at a high frequency to a subsequent electronic circuit. In addition, the light receiving element 600 can perform an output operation suitable for high-intensity light input in which the intensity of input signal light is high.

[1.3 Quantum Efficiency in Photodetector Unit 601]

FIG. 9 shows an example of simulated quantum efficiency in the photodetector unit 601 of the light receiving element 600 . The vertical axis represents quantum efficiency. The horizontal axis represents the PD length of the photodetector unit 601 .

In FIG. 9 , the curve shown by (a) represents the quantum efficiency in the photodetector unit 601 of the light receiving element 600 shown in FIGS. 6 and 7 . In FIG. 9, the quantum efficiency in the photodetector unit 101 of the light receiving element 100 shown in FIGS. 1 and 2 is shown as a curve (b) for comparison.

As is apparent from FIG. 9 , the quantum efficiency of the light receiving element 600 is generally higher than that of the light receiving element 100 . That is, compared with the light receiving element 100, the light receiving element 600 can improve the quantum efficiency by adopting the structures shown in FIGS. 6 and 7 . For example, in order to obtain a quantum efficiency of 80%, approximately 60% of the PD length of the light receiving element 100 is sufficient as the PD length of the light receiving element 600 . Furthermore, for example, with the same PD length of 10 μm, the light receiving element 600 can provide a quantum efficiency about 1.5 times higher than that of the light receiving element 100 .

Therefore, in the light receiving element 600, the efficiency of light absorption in the photodetector unit 601 can be improved.

[1.4 Specific Example of Structure of Light Receiving Element 600]

FIG. 10 is a perspective view showing an example of the structure of a light receiving element 1000 . FIG. 10 shows only the main part of the light receiving element 1000 . The structure of the light receiving element 1000 shown in FIG. 10 is a specific example of the structure of the light receiving element 600 shown in FIG. 6 , and specifically shows a configuration example of each layer of the light receiving element 600 . FIG. 11 is a cross-sectional view of the light receiving element 1000 taken along the dotted line XI-XI in FIG. 10 . FIG. 11 shows the vicinity of the boundary region between the photodetector unit 1001 and the waveguide unit 1011 . FIG. 12A is a cross-sectional view of the light receiving element 1000 along the dotted line XIIA-XIIA in FIG. 10 , showing the vicinity of the mesa structure. FIG. 12B is a cross-sectional view of the light receiving element 1000 along the dotted line XIIB-XIIB in FIG. 10 , showing the vicinity of the mesa structure.

As shown in FIGS. 10 to 12B , the light receiving element 1000 includes, for example, a photodetector unit 1000 disposed over a semi-insulating (hereinafter referred to as SI) InP substrate 1014 and a waveguide unit 1011 disposed over the same SI-InP substrate 1014. . Elements such as Fe used to form deep doping levels are doped in the SI-InP substrate 1014 .

The waveguide unit 1011 has a structure in which an i-InGaAsP core layer 1012 made of i-type InGaAsP having a bandgap wavelength of 1.05 μm and an i-type InP core layer 1012 are laminated from the SI-InP substrate 1014 side. i-InP cladding layer 1013 . The waveguide unit 1011 has a mesa structure including an i-InP cladding layer 1013 and an i-InGaAsP core layer 1012, and has a high mesa waveguide structure in which no semiconductor material is buried on the side surface.

The photodetector unit 1001 has a structure in which an n-InGaAsP semiconductor layer 1002 made of n-type InGaAsP having a bandgap wavelength of 1.3 μm is stacked from the SI-InP substrate 1014 side, made of an InP lattice The i-InGaAs absorption layer 1003 made of matched i-type InGaAs, the p-InP cladding layer 1004 made of p-type InP, and the p-type contact composed of a two-layer structure of p-type InGaAs and InGaAsP Layer 1005.

The photodetector unit 1001 has a mesa structure including a p-type contact layer 1005 , a p-InP cladding layer 1004 , an i-InGaAs absorbing layer 1003 and a part of an n-InGaAsP semiconductor layer 1002 . The photodetector unit 1001 has a high-mesa waveguide structure in which no semiconductor material is buried on the side surface. The n-InGaAsP semiconductor layer 1002, the i-InGaAs absorption layer 1003 and the p-InP cladding layer 1004 form a PIN-type photodiode.

A p-side electrode 1015 is formed over the p-type contact layer 1005 , and an n-side electrode 1016 is formed over the n-InGaAsP semiconductor layer 1002 . A portion of the light receiving element 1000 where the p-side electrode 1015 and the n-side electrode 1016 are not formed is covered with a passivation film 1017 made of a dielectric such as a silicon nitride film. In FIG. 10, the passivation film 1017 is not shown for easy understanding of the structure.

A predetermined voltage is applied between the p-side electrode 1015 and the n-side electrode 1016 with the p-side electrode 1015 at negative potential and the n-side electrode 1016 at positive potential. Thus, photogenerated carriers (holes and electrons) generated by light absorption in the i-InGaAs absorption layer 1003 are detected via the p-InP cladding layer 1004 and the n-InGaAsP semiconductor layer 1002 .

In the waveguide unit 1011, for example, the thickness of the i-InGaAsP core layer 1012 is set to 0.5 μm, and the thickness of the i-InP cladding layer 1013 is set to 1.5 μm. In the photodetector unit 1001, for example, the thickness of the n-InGaAsP semiconductor layer 1002 is set to 0.5 μm, the thickness of the i-InGaAs absorption layer 1003 is set to 0.5 μm, and the p-InP cladding layer 1004 and p The total thickness of the -type contact layer 1005 was set to 1.0 µm.

By setting the thicknesses of the plurality of layers as described above, the i-InGaAsP core layer 1012 of the waveguide unit 1011 can be connected to the side surface of the n-InGaAsP semiconductor layer 1002 of the photodetector unit 1001 . The i-InGaAsP core layer 1012 of the waveguide unit 1011 and the n-InGaAsP semiconductor layer 1002 of the photodetector unit 1001 are connected adjacent to each other along the direction in which the i-InGaAsP core layer 1012 extends.

In waveguide unit 1011, for example, the mesa structure including i-InGaAsP core layer 1012 and i-InP cladding layer 1013 has a width (width in a direction orthogonal to the direction in which i-InGaAsP core layer 1012 extends) of 2.5 μm. In the photodetector unit 1001, the width of the mesa structure including the i-InGaAs absorbing layer 1003, the p-InP cladding layer 1004, and the p-type contact layer 1005 (in the direction perpendicular to the extending direction of the i-InGaAsP core layer 1012 The width of the photodetector unit 1001 (PD length) is 5 μm, and the length (PD length) of the photodetector unit 1001 is 10 μm.

The light receiving element 1000 having the above structure can supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency while improving the efficiency of light absorption in the photodetector unit 1001 . In addition, the light receiving element 1000 can perform an output operation suitable for a high-intensity light input in which the intensity of the input signal light is high.

In the above-described embodiments, as an example of the light receiving element 1000 regarding signal light having a wavelength of about 1.5 μm, a photodiode in which the i-InGaAs absorption layer 1003 is made of InGaAs and a plurality of layers ( Such as the waveguide layer) is made of InGaAsP-based material. However, the embodiment is not limited thereto. In the light receiving element 1000 according to the above-described embodiment, the material of the i-InGaAs absorption layer 1003 may be another material that absorbs light within the wavelength band of the incident signal light, and the material of the other layers may not absorb such light another material.

Although the material of a plurality of layers such as the i-InGaAs absorbing layer 1003 is an i-type semiconductor in the above example, however, for example, part or all of the material of the i-InGaAs absorbing layer 1003 may be p-type or n-type semiconductor.

Although in the above-described embodiments, the high mesa structure is described as a waveguide structure in each of the waveguide unit 1011 and the photodetector unit 1001, the waveguide structure may be such a structure that part or all of the structure is formed as a buried waveguide .

[1.5 Manufacturing method of light receiving element 1000]

FIGS. 13A to 17B are diagrams each showing an example of a manufacturing process of the light receiving element 1000 shown in FIGS. 10 to 12B . In FIGS. 13A to 17B , each of FIGS. 13A , 14A, 15A, 16A, and 17A on the upper side is a plan view showing a light receiving element as viewed from above the corresponding substrate. The main part of 1000. Figure 13B, Figure 14B, Figure 15B, Figure 16B and Figure 17B located on the lower side are respectively along the dotted lines XIIIB-XIIIB, XIVB-XIVB, XVB-XVB, XVIB of the plan view 13A, Figure 14A, Figure 15A, Figure 16A and Figure 17A - Cross-sectional views of XVIB and XVIIB-XVIIB showing the vicinity of the boundary region between the waveguide unit 1011 and the photodetector unit 1001 . Hereinafter, an example of a manufacturing method of the light receiving element 1000 is described with reference to FIGS. 13A to 17B .

As shown in FIG. 13A and FIG. 13B, on the SI-InP substrate 1301, an n-InGaAsP film 1302, an i-InGaAs film 1303, a p-InP film 1304, and The p-InGaAs/InGaAsP laminated film 1305 is composed of two films of p-InGaAs and InGaAsP. At this time, the deposition is performed so that the n-InGaAsP film 1302 has a thickness of 0.5 μm and the i-InGaAs film 1303 has a thickness of 0.5 μm. Furthermore, this deposition is performed so that the total thickness of the p-InP film 1304 and the p-InGaAs/InGaAsP laminated film 1305 becomes 1.0 μm.

Next, a mask 1401 is formed over the p-InGaAs/InGaAsP laminated film 1305 to cover the region to be the photodetector unit 1001 as shown in FIGS. 10 and 12B , thereby selectively exposing the region to be the waveguide unit 1011 . For example, a silicon oxide film is used as the mask 1401 . By using the mask 1401 to etch according to the prior art, as shown in FIGS. 14A and 14B, only the n-InGaAsP film 1302, the i-InGaAs film 1303, the p-InP film 1304, and the p-InGaAsP film 1304 and p- InGaAs/InGaAsP laminated films 1305, and these films are removed from the waveguide unit 1011. Through this process, in the waveguide unit 1011, the SI-InP substrate 1301 is exposed.

Next, as shown in FIGS. 15A and 15B, over the exposed SI-InP substrate 1301 (from its waveguide unit 1011), i-InGaAsP films 1501 and i-InGaAsP films 1501 and i - InP film 1502 . At this time, the deposition was performed so that the i-InGaAsP film 1501 had a thickness of 0.5 μm and the i-InP film 1502 had a thickness of 0.5 μm. Since the photodetector unit 1001 is covered with the mask 1401 used in the above-described etching, the growth of the i-InGaAsP film 1501 and the i-InP film 1502 in the photodetector unit 1001 can be suppressed. After depositing the i-InP film 1502, the mask 1401 is removed.

Next, a mask is formed over p-InGaAs/InGaAsP laminated film 1305 and i-InP film 1502 for covering a region to be a mesa structure in each of photodetector unit 1001 and waveguide unit 1011 . For example, a silicon oxide film is used as a mask. By performing etching according to the prior art using this mask, a mesa structure is formed in each of the photodetector unit 1001 and the waveguide unit 1011 . After etching, the mask is removed.

At this time, as shown in FIGS. 16A and 16B , in the photodetector unit 1001, the above mask is used to remove the p-InGaAs/InGaAsP laminated film 1305, the p-InP film 1304, and the i-InGaAs film 1303, and the n - InGaAsP film 1302 is removed half its depth to leave part of n-InGaAsP film 1302 . Through this process, part of the n-InGaAsP film 1302 is exposed. Thus, a mesa structure is formed as shown in FIG. 10 to FIG. 12B , which includes a part of n-InGaAsP semiconductor layer 1002 , i-InGaAs absorption layer 1003 , p-InP cladding 1004 and p-type contact layer 1005 .

As shown in FIG. 16A and FIG. 16B, in the waveguide unit 1011, the above-mentioned mask is used to remove the i-InP film 1502 and the i-InGaAsP film 1501, and the part of the SI-InP substrate 1301 located under the i-InGaAsP film 1501 is also be removed. Through this process, part of the SI-InP substrate 1301 is exposed. Thus, the mesa structure including the i-InGaAsP core layer 1012 and the i-InP cladding 1013 shown in FIGS. 10 to 12B is formed.

Next, in the photodetector unit 1001 and the waveguide unit 1011, a passivation film 1017 made of a dielectric (such as a silicon nitride film) is formed except for a region where electrodes are to be formed. After that, as shown in FIGS. 17A and 17B, in the photodetector unit 1001, a p-side electrode 1015 is formed on the exposed p-type contact layer 1005 by a method according to the prior art, such as metal deposition or electroplating. In the area at the top of the table top structure. Furthermore, an n-side electrode 1016 is formed in a region where the n-InGaAsP semiconductor layer 1002 is exposed by a method according to the prior art, such as metal deposition or plating. In the plan view of FIG. 17A , the passivation film 1017 is not shown for easy understanding of the structure.

In FIGS. 17A and 17B , an electrode having an air bridge structure is used as the p-side electrode 1015 . As is apparent from the cross-sectional view of FIG. 17B, due to this structure, the n-InGaAsP semiconductor layer 1012 to which the p-side electrode 1015 and the n-side electrode 1016 are connected is electrically insulated by air.

Thus, the parasitic capacitance generated between the p-side electrode 1015 and the n-side electrode 1016 can be reduced. Therefore, the capacitance of the photodetector unit 1001 can be further reduced. Thus, the light receiving element 1000 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a higher frequency.

However, the structure of the p-side electrode 1015 is not limited to the air bridge structure. An insulator may be formed in advance where the p-side electrode 1015 is to be formed, and then the p-side electrode 1015 may be formed over the insulator. In FIGS. 17A and 17B , n-InGaAsP semiconductor layer 1002 partially remains in a portion of PD opposite to waveguide unit 1011 , and p-side electrode 1015 is formed over n-InGaAsP semiconductor layer 1002 via passivation film 1017 . However, it is also possible to remove the n-InGaAsP semiconductor layer 1002 in the portion of the PD opposite to the waveguide unit 1011 . This can reduce the capacitance of the p-side electrode 1015, and also further improve the characteristics at high frequencies.

Although not shown in FIGS. 15A and 15B , in practice, there is a case where the i-InGaAsP film 1501 is also deposited in a small thickness on the photodetector unit 1001 exposed by etching as shown in FIGS. 14A and 14B . condition on the side wall section. However, the film deposited on the sidewall portion of the photodetector unit 1001 is sufficiently thinner than that of the i-InGaAsP core layer 1012, and the refractive index of the film deposited on the sidewall portion is also different from that of the i-InGaAsP core layer 1012. same rate. Therefore, this film does not affect the propagation of signal light.

[2. Second embodiment]

FIG. 18 is a diagram showing an example of the structure of a light receiving element 1800 according to the second embodiment. FIG. 18 shows a section corresponding to that of the light receiving element 600 according to the first embodiment as shown in FIG. 7 . The light receiving element 1800 shown in FIG. 18 is different from the light receiving element 600 shown in FIG. 6 in the thickness of the core, but otherwise the same. Since the perspective view of the light receiving element 1800 is the same as that of the light receiving element 600 shown in FIG. 6 except for the thickness of the core, the perspective view is not shown.

As shown in FIG. 18 , the light receiving element 1800 includes a photodetector unit 1801 provided over a substrate 1814 and a waveguide unit 1811 provided over the same substrate 1814 .

The waveguide unit 1811 has a structure in which a core 1812 and an upper cladding layer 1813 are laminated from the substrate 1814 side. The material of each layer of the stacked structure is, for example, semiconductor. The waveguide unit 1811 has a mesa structure including an upper clad layer 1813 and a core 1812 . The signal light propagates in the core 1812 and enters the photodetector unit 1801 .

Photodetector unit 1801 has a structure in which n-type semiconductor layer 1802, i-type absorption layer 1803, p-type upper cladding layer 1804, and p-type contact layer 1805 are stacked from the substrate 1814 side. Each material of each layer of the stacked structure is, for example, a semiconductor. The photodetector unit 1801 has a mesa structure including a p-type contact layer 1805 , a p-type upper cladding layer 1804 , an i-type absorbing layer 1803 , and part of an n-type semiconductor layer 1802 . The n-type semiconductor layer 1802, the i-type absorber layer 1803 and the p-type upper cladding layer 1804 form a PIN-type photodiode.

As shown in FIG. 18, in light receiving element 1800, core 1812 is connected to the side surface of n-type semiconductor layer 1802, and core 1812 and n-type semiconductor layer 1802 are connected adjacent to each other in the direction in which core 1812 extends. The core 1812 is formed such that its top surface is set higher than the bottom surface of the n-type semiconductor layer 1802 (set farther from the substrate 1814), and its bottom surface is set lower than the top surface of the n-type semiconductor layer 1802 ( set closer to the substrate 1814).

The n-type semiconductor layer 1802 is formed such that its refractive index is higher than that of the core 1812 and lower than that of the i-type absorbing layer 1803 . That is, n-type semiconductor layer 1802 is formed such that its bandgap wavelength is longer than that of core 1812 and shorter than that of i-type absorbing layer 1803 . The n-type semiconductor layer 1802 is formed to have a composition such that the absorption coefficient for signal light is sufficiently small.

Furthermore, as shown in FIG. 18, in light receiving element 1800, core 1812 is formed such that its top surface is set lower than the top surface of n-type semiconductor layer 1802 (set closer to substrate 1814). The bottom surface of core 1812 is flush with the bottom surface of n-type semiconductor layer 1802 . For example, the structure shown in FIG. 18 can be formed by making the thickness of the core 1812 smaller than that of the n-type semiconductor layer 1802 .

As shown in FIG. 18 , in light receiving element 1800 , signal light propagates in core 1812 in waveguide unit 1811 , and enters n-type semiconductor layer 1802 in photodetector unit 1801 . The n-type semiconductor layer 1802 receives signal light from the core 1812 along the direction in which the core 1812 extends. Since the refractive index of the n-type semiconductor layer 1802 is set higher than that of the core 1812, loss when signal light enters the n-type semiconductor layer 1802 from the core 1812 can be reduced. Part of the incident signal light permeates from the n-type semiconductor layer 1802 into the i-type absorbing layer 1803 and is absorbed in the i-type absorbing layer 1803 .

In the photodetector unit 1801, unlike in the photodetector unit 101 of the light receiving unit 100 shown in FIG. 1 and FIG. n-type semiconductor layer 1802. Therefore, as soon as the signal light enters the n-type semiconductor layer 1802, the signal light penetrates into the i-type absorption layer 1803, and its absorption starts. Therefore, in the photodetector unit 1801, the PD length can be made shorter than the PD length of the photodetector unit 101 in the light receiving unit 100 while ensuring sufficient light absorption efficiency.

Since the PD length of the photodetector unit 1801 can be shortened, the capacitance of the photodetector unit 1801 can be reduced. Therefore, the light receiving element 1800 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency, thereby enabling the subsequent electronic circuit to process an input signal also at a high frequency.

Furthermore, in the light receiving element 1800, unlike in the photodetector unit 301 of the light receiving element 300 shown in FIGS. The i-type semiconductor layer 1802, and then its component that penetrates into the i-type absorbing layer 1803 is absorbed. Therefore, in the photodetector unit 1801 , the overall concentration distribution of generated photo-generated carriers is a flat, slightly inclined distribution compared to that in the photodetector unit 301 .

Furthermore, in light receiving element 1800 , unlike in light receiving element 600 shown in FIG. 7 , the top surface of core 1812 is positioned lower than the top surface of n-type semiconductor layer 1802 . Therefore, in the light receiving element 1800, compared with the light receiving element 600, the signal light penetrating into the i-type absorbing layer 1803 becomes less, and the amount corresponding to the top surface of the core 1812 and the top surface of the n-type semiconductor layer 1802 is reduced. The amount of difference between surfaces. That is, the absorption per unit length in the i-type absorbing layer 1803 becomes smaller than in the case of the light receiving element 600, and the propagation distance of signal light where sufficient absorption occurs becomes longer than in the case of the light receiving element 600 long.

Therefore, the peak of the photogenerated carrier concentration distribution in the photodetector unit 1801 of the light receiving element 1800 occurs at a distance from the end face of the photodetector unit 1801 (signal light from which to enter) further away. Therefore, in the light receiving element 1800, the overall concentration distribution of the generated photogenerated carriers extends to a position farther from the end face of the photodetector unit 1801, and thus, compared with the distribution in the case of the light receiving element 600, for a flatter, slightly more sloped distribution. The concentration value at the peak position of the photogenerated carrier concentration distribution becomes smaller than the concentration value at the peak position in the case of the light receiving element 600 .

Therefore, in the photodetector unit 1801 of the light receiving element 1800 compared with the photodetector unit 601, when signal light having a higher intensity is input, an excessive increase in local photogenerated carrier concentration can also be reduced. More. Therefore, in the photodetector unit 1801, degradation of high-frequency characteristics of high-intensity signal light can be reduced. Thus, in the light receiving element 1800 , compared with the light receiving element 600 , an output operation suitable for input of signal light having a higher intensity can be performed.

As described above, in the light receiving element 1800 according to the second embodiment, while improving the light absorption efficiency in the photodetector unit 1801, a detection signal having a sufficient signal level can be supplied at a high frequency. to the subsequent electronic circuit. In addition, the light receiving element 1800 can perform an output operation suitable for high-intensity light input in which the intensity of input signal light is high.

Furthermore, the light receiving element 1800 according to the second embodiment can also be adapted to input signal light having a higher intensity than the light receiving element 600 according to the first embodiment. For example, the light-receiving element 1800 according to the second embodiment is effectively applied to a light-receiving element, a light-receiving device, and a light-receiving module that process signal light having a relatively high intensity, and using these light-receiving elements, light-receiving devices, and light-receiving A system of modules.

As a specific example of the structure of the light receiving element 1800 of the second embodiment, the configuration described above as a specific example of the structure of the light receiving element 600 according to the first embodiment can be used. However, as described above, core 1812 is formed such that its thickness is smaller than that of n-type semiconductor layer 1802 .

For the manufacturing method of the light receiving element 1800, the method described above as the manufacturing method of the light receiving element 600 can be used.

[3. The third embodiment]

[3-1. Structure of light receiving element 1900 ]

FIG. 19 shows an example of the structure of a light receiving element 1900 according to the third embodiment. FIG. 19 shows a cross section corresponding to that of the light receiving element 600 according to the first embodiment shown in FIG. 7 . The light receiving element 1900 shown in FIG. 19 is different from the light receiving element 600 shown in FIG. 6 in the thickness of the core, but otherwise the same. Since the perspective view of the light receiving element 1900 is the same as that of the light receiving element 600 shown in FIG. 6 except that the thickness of the core is different, the perspective view is not shown.

As shown in FIG. 19 , the light receiving element 1900 includes a photodetector unit 1901 provided over a substrate 1914 and a waveguide unit 1911 provided over the same substrate 1914 .

The waveguide unit 1911 has a structure in which a core 1912 and an upper cladding layer 1913 are laminated from the substrate 1914 side. The material of each layer of the stacked structure is, for example, semiconductor. The waveguide unit 1911 has a mesa structure including an upper clad layer 1913 and a core 1912 . The signal light is caused to propagate in the core 1912 and enter the photodetector unit 1901 .

Photodetector unit 1901 has a structure in which n-type semiconductor layer 1902, i-type absorption layer 1903, p-type upper cladding layer 1904, and p-type contact layer 1905 are stacked from the substrate 1914 side. The material of each layer of the stacked structure is, for example, semiconductor. The photodetector unit 1901 has a mesa structure including a p-type contact layer 1905 , a p-type upper cladding layer 1904 , an i-type absorbing layer 1903 , and part of an n-type semiconductor layer 1902 . The n-type semiconductor layer 1902, the i-type absorber layer 1903 and the p-type upper cladding layer 1904 form a PIN-type photodiode.

In light receiving element 1900 shown in FIG. 19 , core 1912 is connected to side surfaces of n-type semiconductor layer 1902 and i-type absorbing layer 1903 . Core 1912 is connected adjacent to each other with n-type semiconductor layer 1902 and i-type absorption layer 1903 in the direction in which core 1912 extends. The core 1912 is formed such that its top surface is set higher than the bottom surface of the n-type semiconductor layer 1902 (set farther from the substrate 1914), and its bottom surface is set lower than the top surface of the n-type semiconductor layer 1902 ( set closer to the substrate 1914).

The n-type semiconductor layer 1902 is formed such that its refractive index is higher than that of the core 1912 and lower than that of the i-type absorbing layer 1903 . That is, n-type semiconductor layer 1902 is formed such that its bandgap wavelength is longer than that of core 1912 and shorter than that of i-type absorbing layer 1903 . The n-type semiconductor layer 1902 is formed to have a composition such that the absorption coefficient for signal light is sufficiently small.

Furthermore, as shown in FIG. 19, in the light receiving element 1900, the core 1912 is formed such that its top surface is set higher than the top surface of the n-type semiconductor layer 1902 (set farther from the substrate 1914), and lower on the top surface of the i-type absorber layer 1903 (disposed closer to the substrate 1914). The bottom surface of core 1912 is flush with the bottom surface of n-type semiconductor layer 1902 . For example, the structure shown in FIG. 19 can be formed by making the thickness of the core 1912 larger than that of the n-type semiconductor layer 1902 .

However, it is preferable that the thickness of the n-type semiconductor layer 1902 is not less than half the thickness of the core 1912 . That is, it is preferable that the thickness of the portion of the core 1912 connected to the i-type absorbing layer 1903 is not more than half of the entire thickness of the core 1912 . In addition, it is preferable that half or more of the core 1912 with respect to the thickness direction be disposed lower than the top surface of the n-type semiconductor layer 1902 (disposed closer to the substrate 1914 ). In addition, it is preferable that the thickness of the core 1912 is smaller than the sum of the thickness of the i-type absorption layer 1903 and the thickness of the n-type semiconductor layer 1902 . This is to ensure that the photodetector unit is performed substantially equally or primarily by penetrating the signal light from the n-type semiconductor layer 1902 into the i-type absorbing layer 1903 compared to the direct entry of signal light into the i-type absorbing layer 1903. The light in 1901 is absorbed, so that the value of the photogenerated carrier concentration near the end face of the photodetector unit 1901 does not become extremely large. Details on this point are given below.

As shown in FIG. 19, in the light receiving element 1900, the signal light propagates in the core 1912 in the waveguide unit 1911, and in the photodetector unit 1901, most of the signal light enters the n-type semiconductor layer 1902, and the signal The rest of the light enters the i-type absorbing layer 1903 directly. The n-type semiconductor layer 1902 and the i-type absorption layer 1903 receive signal light from the core 1912 along the direction in which the core 1912 extends. Since the refractive index of the n-type semiconductor layer 1902 and the i-type absorption layer 1903 is set to be higher than that of the core 1912, the signal light entering the n-type semiconductor layer 1902 and the i-type absorption from the core 1912 can be reduced. Loss at layer 1903. Part of the signal light that has entered n-type semiconductor layer 1902 permeates from n-type semiconductor layer 1902 into i-type absorption layer 1903, and is absorbed into i-type absorption layer 1903. The signal light that has entered the i-type absorption layer 1903 is absorbed while it is in a region near the end face of the i-type absorption layer 1903 from which the signal light enters.

In the photodetector unit 1901, unlike the photodetector unit 101 of the light receiving unit 100 shown in FIGS. n-type semiconductor layer 1902 . Therefore, as soon as the signal light enters the n-type semiconductor layer 1902, most of the signal light permeates into the i-type absorption layer 1903, and the absorption of the signal light starts immediately after entering. Therefore, in the photodetector unit 1901, the PD length can be made shorter than the PD length of the photodetector unit 101 in the light receiving element 100 while ensuring sufficient light absorption efficiency.

Since the PD length of the photodetector unit 1901 can be shortened, the capacitance of the photodetector unit 1901 can be reduced. Therefore, the light receiving element 1900 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency. This enables subsequent electronic circuits to process the input signal also at high frequencies.

Furthermore, in the light receiving element 1900 , unlike in the light receiving element 600 shown in FIG. 7 , part of the signal light directly enters the i-type absorbing layer 1903 . Since the absorption of incident signal light occurs in a region near the end face of i-type absorbing layer 1903 from which signal light enters, the concentration value of photogenerated carriers near the end face of photodetector unit 1901 can be increased. Thus, in the light receiving element 1900 , the efficiency of light absorption in the photodetector unit 1901 can be further improved compared to the photodetector unit 601 . Therefore, the light receiving element 1900 can also be adapted to input signal light having a lower intensity than the light receiving element 600 without increasing the PD length.

Furthermore, in the light receiving element 1900 , further improving the light absorption efficiency can further shorten the PD length of the photodetector unit 1901 , compared with the light receiving element 600 . Further shortening the PD length can further reduce the capacitance of the photodetector unit 1901 . Therefore, the light receiving element 1900 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a higher frequency. This enables subsequent electronic circuits to also process the input signal at higher frequencies.

On the other hand, in the light receiving element 1900, unlike in the photodetector unit 301 of the light receiving element 300 shown in FIG. Therefore, the concentration value of photogenerated carriers does not become extremely large near the end face of the photodetector unit 1901 (from which the signal light enters). Therefore, in the photodetector unit 1901, even in the case of high-intensity light input in which the intensity of input signal light is high, an excessive increase in local photogenerated carrier concentration can be reduced. Thus, in the light receiving element 1900, it is possible to reduce degradation of high-frequency characteristics of high-intensity signals.

As described above, in the light receiving element 1900 according to the third embodiment, while improving the light absorption efficiency in the photodetector unit 1901, it is also possible to supply a detection signal having a sufficient signal level at a high frequency to subsequent electronic circuit. In addition, the light receiving element 1900 can perform an output operation suitable for a high-intensity light input in which the intensity of input signal light is high.

Furthermore, in the light receiving element 1900 according to the third embodiment, the light absorption efficiency can be further improved as compared with the light receiving element 600 according to the first embodiment. Thus, the light receiving element 1900 can also be adapted to detect signal light having a lower intensity without increasing the PD length. In addition, the light receiving element 1900 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency.

For example, the light-receiving element 1900 according to the third embodiment can be effectively applied to a light-receiving element, a light-receiving device, and a light-receiving module that process signal light having a relatively low intensity, and using these light-receiving elements, light-receiving devices, and light The system that receives the module. Furthermore, the light receiving element 1900 according to the third embodiment can be effectively applied to light receiving elements, light receiving devices, and light receiving modules for which electronic circuits operating at higher operating frequencies are arranged in subsequent stages ), and a system using these light-receiving elements, light-receiving devices, and light-receiving modules.

As a specific example of the structure of the light receiving element 1900 of the third embodiment, the configuration described above as a specific example of the structure of the light receiving element 600 according to the first embodiment can be used. However, as described above, the core 1912 is formed to have a thickness greater than that of the n-type semiconductor layer 1902

For the manufacturing method of the light receiving element 1900, the method described above as the manufacturing method of the light receiving element 600 can be used.

[3-2 Photogenerated Carrier Concentration Distribution in Photodetector Unit 1901]

FIG. 20 shows one example of a simulated concentration distribution of photogenerated carriers generated in the photodetector unit 1901 of the light receiving element 1900 . The vertical axis represents the concentration of photogenerated carriers when normalized based on a predetermined value. The horizontal axis represents the position within the PD in the photodetector unit 1901 .

In FIG. 20 , the curves shown by (d) to (f) represent the photogenerated carrier concentration distribution in the photodetector unit 1901 of the light receiving element 1900 shown in FIG. 19 . The distribution curve shown by (d) represents the distribution in the case where the thickness of the portion of the core 1912 connected to the i-type absorbing layer 1903 is set to 25% of the total thickness of the core 1912 . The distribution curve shown by (e) represents the distribution in the case where the thickness of the portion of the core 1912 connected to the i-type absorbing layer 1903 is set to 50% of the total thickness of the core 1912 . The distribution curve shown by (f) represents the distribution in the case where the thickness of the portion of the core 1912 connected to the i-type absorbing layer 1903 is set to 75% of the total thickness of the core 1912 .

In FIG. 20, for comparison, the photogenerated carrier concentration distribution curve (b) of the photodetector unit 301 of the light receiving element 300 shown in FIG. The photogenerated carrier concentration distribution curve (c) of the photodetector unit 601 of the element 600 is represented by alternate long and short dash lines. The photogenerated carrier concentration distribution curve (b) corresponds to the case where the thickness of the part connected to the i-type absorption layer 1903 in the core 1912 is set as 100% of the total thickness of the core 1912, and the photogenerated carrier concentration distribution curve (c) corresponds to the case where the thickness of the portion of the core 1912 connected to the i-type absorbing layer 1903 is set to 0% of the total thickness of the core 1912 .

[3-2-1 Comparison between the cases where the thickness of the portion where the core 1912 is connected to the i-type absorbing layer 1903 is different]

The photogenerated carrier concentration distribution in the photodetector unit 1901 was compared between cases where the thickness of the portion of the core 1912 connected to the i-type absorbing layer 1903 was different.

As represented by the distribution curve (d) in Figure 20, under the condition that the thickness of the part where the core 1912 is connected to the i-type absorber layer 1903 is set to be 25% of the total thickness of the core 1912, the photogenerated carrier concentration The peak of the distribution occurs at a position spaced a predetermined distance from the end face of the photodetector unit 1901 from which the signal light enters.

In the distribution curve (d), the peak value of the photogenerated carrier concentration distribution is compared with the maximum value (concentration near the end face of the photodetector unit 1901) in the case of the distribution curve (b) (light receiving element 300) The concentration value at the position is sufficiently small. In addition, the overall concentration distribution is a flat, slightly inclined distribution compared with the distribution curve (b) (light receiving element 300 ).

That is, profile (d) has characteristics more similar to profile (c) (light receiving element 600 ) than profile (b) (light receiving element 300 ). Therefore, in this case, it is considered that, as in the case of the distribution curve (c) (light receiving element 600), the signal light mainly penetrates from the n-type semiconductor layer 1902 to the i-type absorption layer 1903, rather than passing the signal light. Light directly enters the i-type absorbing layer 1903 to perform light absorption in the photodetector unit 1901 .

On the other hand, as represented by the distribution curve (f) in FIG. The maximum value of the photogenerated carrier concentration distribution occurs from the end face of the photodetector unit 1901 (from which the signal light enters), and the photogenerated carrier concentration distribution is concentrated in the vicinity of the end face. Therefore, although lower than the distribution curve (b) (light receiving element 300), the photogenerated carrier concentration is still high.

That is, profile (f) has characteristics more similar to profile (b) (light receiving element 300 ) than profile (c) (light receiving element 600 ). Therefore, in this case, it is considered that, as in the case of the distribution curve (b) (light receiving element 300), the signal light directly enters the i-type absorbing layer 1903 mainly, rather than passing the signal light from the n-type semiconductor layer 1902. Infiltrated into the i-type absorbing layer 1903 to perform light absorption in the photodetector unit 1901.

On the contrary, as represented by the distribution curve (e) in FIG. At positions separated by a predetermined distance from the end face of the photodetector unit 1901 from which the signal light enters, a small peak in the photogenerated carrier concentration distribution appears, and a slightly higher peak is observed in a region near the end face of the photodetector unit 1901. Photogenerated carrier concentration.

In the case of the distribution curve (e), unlike the distribution curve (b) (light receiving element 300) or the above-mentioned distribution curve (f), the photogenerated carrier concentration distribution has a relative flat shape. As a result, in the case of the distribution curve (e), the maximum value of the photogenerated carrier concentration decreases to the maximum value in the case of the distribution curve (b) (light receiving element 300) (concentration near the end face of the photodetector unit 301 ) about (roughly) half of.

That is, the characteristic of the profile (e) is approximately in the middle of the characteristics of the profile (c) (the light receiving element 600 ) and the profile (b) (the light receiving element 300 ). Therefore, in this case, it is considered that between the signal light penetrates from the n-type semiconductor layer 1902 into the i-type absorbing layer 1903 and the signal light directly enters the i-type absorbing layer 1903, the light in the n-type semiconductor layer 1902 The absorption contribution ratio is basically the same.

It will be appreciated from the above that the thickness of the portion of the core 1912 connected to the i-type absorber layer 1903 is preferably no more than half of the total thickness of the core 1912 . This can ensure that the photodetector unit 1901 is performed substantially equally or mainly by signal light penetrating from the n-type semiconductor layer 1902 into the i-type absorbing layer 1903 compared to the signal light directly entering the i-type absorbing layer 1903. light absorption in . Thus, even in the case of high-intensity light input in which the intensity of input signal light is high, an excessive increase in local photogenerated carrier concentration can be reduced.

[3-2-2 Comparison with Light Receiving Element 600 (Concentration Profile (c))]

Next, regarding the case where the thickness of the portion of the core 1912 connected to the i-type absorbing layer 1903 is set to 25% of the total thickness of the core 1912 (concentration profile (d) in FIG. 20 ), between the light receiving element 1900 and The photogenerated carrier concentration distributions in the photodetector cells 1901 , 601 are compared between the light receiving elements 600 .

In the case of the distribution curve (d) in FIG. 20, the position of the peak of the photogenerated carrier concentration distribution is closer to the end face of the photodetector unit 1901 (signal light enters through it). Therefore, the overall photogenerated carrier concentration distribution is also shifted to the side closer to the end face of the photodetector unit 1901, and the extension of the distribution as a whole is also small.

Thus, in the light receiving element 1900 , the efficiency of light absorption can be further improved compared with the light receiving element 600 . Thus, the light receiving element 1900 can also be adapted to detect signal light having a lower intensity without increasing the PD length.

Furthermore, in the light receiving element 1900 , further improving the light absorption efficiency can further shorten the PD length of the photodetector unit 1901 as compared with the light receiving element 600 . Further shortening the PD length can further reduce the capacitance of the photodetector unit 1901 . Therefore, the light receiving element 1900 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a higher frequency.

As described above, in the light receiving element 1900 according to the third embodiment, the light absorption efficiency can be further improved compared with the light receiving element 600 according to the first embodiment. Thus, the light receiving element 1900 can also be adapted to detect signal light having a stronger density without increasing the PD length. In addition, the light receiving element 1900 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a higher frequency.

[4. Fourth Embodiment]

FIG. 21 shows an example of the structure of a light receiving element 2100 according to the fourth embodiment. FIG. 21 shows a cross section corresponding to that of the light receiving element 600 according to the first embodiment shown in FIG. 7 . The light receiving element 2100 shown in FIG. 21 differs from the light receiving element 1900 shown in FIG. 19 in the buffer layer formed between the substrate and the core, but is otherwise the same. A perspective view of the light receiving element 2100 is not shown as in the case of the light receiving element 1900 shown in FIG. 19 .

As shown in FIG. 21 , the light receiving element 2100 includes a photodetector unit 2101 provided over a substrate 2114 and a waveguide unit 2111 provided over the same substrate 2114 .

The waveguide unit 2111 has a structure in which a buffer layer 2115, a core 2112, and an upper cladding layer 2113 are stacked from the substrate 2114 side. The material of each layer of the stacked structure is, for example, semiconductor. The waveguide unit 2111 has a mesa structure including a buffer layer 2115 , an upper cladding layer 2113 and a core 2112 . The signal light propagates in the core 2112 and enters the photodetector unit 2101 .

The reason for why the buffer layer 2115 is provided between the substrate 2114 and the core 2112 is that if the core 2112 is directly formed on the surface of the substrate 2114, then such a situation may occur that when deposited on the surface of the substrate 2114 becomes the core 2112 When a film is used, defects can occur within the film making it difficult for the core 2112 to obtain acceptable film quality. A buffer layer 2115 is provided to avoid this.

As shown in FIG. 21 , the buffer layer 2115 also remains in the sidewall portion of the photodetector unit 2101 for reasons related to the manufacturing process. That is, the buffer layer 2115 is also inserted between the n-type semiconductor layer 2102 and the i-type absorption layer 2103 . In general, the buffer layer 2115 is formed of a material with a lower index of refraction than the core 2112 . Therefore, when the signal light that has propagated through the core 2112 enters the n-type semiconductor layer 2102 and the i-type absorption layer 2103, loss of the signal light occurs in the buffer layer 2115. In order to reduce this loss, it is preferable to form the buffer layer 2115 as thin as possible.

Photodetector unit 2101 has a structure in which n-type semiconductor layer 2102, i-type absorption layer 2103, p-type upper cladding layer 2104, and p-type contact layer 2105 are laminated from the substrate 2114 side. The material of each layer of the stacked structure is, for example, semiconductor. The photodetector unit 2101 has a mesa structure including a p-type contact layer 2105 , a p-type upper cladding layer 2104 , an i-type absorption layer 2103 , and part of an n-type semiconductor layer 2102 . The n-type semiconductor layer 2102, the i-type absorber layer 2103 and the p-type upper cladding layer 2104 form a PIN-type photodiode.

Core 2112 is connected to the side surface of n-type semiconductor layer 2102 and the side surface of i-type absorption layer 2103 via buffer layer 2115 . The core 2112 and the n-type semiconductor layer 2102 and the i-type absorption layer 2103 are connected adjacent to each other via the buffer layer 2115 in the direction in which the core 2112 extends. The core 2112 is formed such that its top surface is set higher than the bottom surface of the n-type semiconductor layer 2102 (set farther from the substrate 2114), and its bottom surface is set lower than the top surface of the n-type semiconductor layer 2102 ( set farther from the substrate 2114).

In this specification, the case where the core is connected to the side surface of the n-type semiconductor layer or the side surface of the i-type absorption layer also includes the case where the core is connected to the side surface of the n-type semiconductor layer or the i-type absorption layer via the buffer layer condition of the side surface.

The n-type semiconductor layer 2102 is formed such that its refractive index is higher than that of the core 2112 and lower than that of the i-type absorbing layer 2103 . That is, n-type semiconductor layer 2102 is formed such that its bandgap wavelength is longer than that of core 2112 and shorter than that of i-type absorbing layer 2103 . The n-type semiconductor layer 2102 is formed to have a composition such that the absorption coefficient for signal light is sufficiently small.

In addition, as shown in FIG. 21, the core 2112 is formed such that its top surface is disposed higher than the top surface of the n-type semiconductor layer 2102 (disposed farther from the substrate 2114), and lower than the i-type absorption layer 2103. The top surface of (set closer to the substrate 2114). The bottom surface of core 2112 is higher than the bottom surface of n-type semiconductor layer 2102 (disposed farther from substrate 2114), and lower than the top surface of n-type semiconductor layer 2102 (disposed closer to substrate 2114). The bottom surface of the buffer layer 2115 is flush with the bottom surface of the n-type semiconductor layer 2102 . The structure shown in FIG. 21 can be formed, for example, by making the thickness of the laminate including the core 2112 and the buffer layer 2115 larger than that of the n-type semiconductor layer 2102 .

However, it is preferable that the thickness of the n-type semiconductor layer 2102 is not less than half the thickness of the core 2112 . That is, it is preferable that the thickness of the portion where the core 2112 is connected to the i-type absorbing layer 2103 is not more than half of the entire thickness of the core 2112 . This is to ensure that light absorption in the photodetector unit 2101 is performed mainly by signal light penetrating from the n-type semiconductor layer 2102 to the i-type absorbing layer 2103, rather than by directly entering the i-type absorbing layer 2103 by signal light. , so that the value of the photogenerated carrier concentration near the end face of the photodetector unit 2101 does not become extremely large. Details on this point are as described above with reference to the third embodiment.

As shown in FIG. 21, in the light receiving element 2100, the signal light propagates in the core 2112 in the waveguide unit 2111, and in the photodetector unit 2101, most of the signal light enters the n-type semiconductor layer 2102, and the signal The rest of the light enters the i-type absorbing layer 2103 directly. The n-type semiconductor layer 2102 and the i-type absorption layer 2103 receive signal light from the core 2112 along the direction in which the core 2112 extends. Part of the signal light that has entered n-type semiconductor layer 2102 permeates from n-type semiconductor layer 2102 into i-type absorption layer 2103, and is absorbed into i-type absorption layer 2103. The signal light that has directly entered the i-type absorption layer 2103 is absorbed while it is in a region near the end face of the photodetector unit 2101 from which the signal light enters.

In the photodetector unit 2101, like in the photodetector unit 1901 of the light receiving unit 1900 shown in FIG. Semiconductor layer 2102. Therefore, in the photodetector unit 2101, as soon as most of the signal light enters the n-type semiconductor layer 2102, the signal light permeates into the i-type absorption layer 2103, and the absorption of the signal light starts immediately after entering. Therefore, in the photodetector unit 2101, the PD length can be made shorter than the PD length of the photodetector unit 101 in the light receiving element 100 while ensuring sufficient light absorption efficiency.

Since the PD length of the photodetector unit 2101 can be shortened, the capacitance of the photodetector unit 2101 can be reduced. Therefore, the light receiving element 2100 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency. This enables subsequent electronic circuits to process the input signal also at high frequencies.

Furthermore, in the light receiving element 2100 , as in the photodetector unit 1901 of the light receiving element 1900 , part of the signal light directly enters the i-type absorbing layer 2103 . Since the absorption of incident signal light occurs in a region near the end face of i-type absorbing layer 2103 from which the signal light enters, the photogenerated carrier concentration value near the end face of photodetector unit 2101 can be increased. Thus, in the light receiving element 2100 , the efficiency of light absorption in the photodetector unit 2101 can be further increased compared with the photodetector unit 601 of the light receiving element 600 shown in FIG. 7 . Therefore, the light receiving element 2100 can also be adapted to input signal light having a lower intensity than the light receiving element 600 without increasing the PD length.

Furthermore, in the light receiving element 2100 , further improving the light absorption efficiency can further shorten the PD length of the photodetector unit 2101 as compared with the light receiving element 600 . Further shortening the PD length can further reduce the capacitance of the photodetector unit 2101 . Therefore, the light receiving element 2100 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a higher frequency. This enables subsequent electronic circuits to also process the input signal at higher frequencies.

On the other hand, in the light receiving element 2100, unlike in the photodetector unit 301 of the light receiving element 300 shown in FIG. 4, only part of the signal light directly enters the i-type absorbing layer 2103. Therefore, the concentration value of photogenerated carriers does not become very large in the vicinity of the end face of the photodetector unit 2101 (from which the signal light enters). Therefore, in the photodetector unit 2101, even in the case of high-intensity light input in which the intensity of input signal light is high, an excessive increase in local photogenerated carrier concentration can be reduced. Thus, in the light receiving element 2100, it is possible to reduce degradation of high-frequency characteristics of high-intensity signals.

As has been described above, in the light receiving element 2100 according to the fourth embodiment, as in the case of the light receiving element 1900 according to the third embodiment, it is possible to improve the light absorption efficiency in the photodetector unit 2101 , can also supply the detection signal with sufficient signal level to the subsequent electronic circuit at high frequency. In addition, the light receiving element 2100 can perform an output operation suitable for a high-intensity light input in which the intensity of input signal light is high.

Furthermore, in the light receiving element 2100 according to the fourth embodiment, the light absorption efficiency can be further increased compared with the light receiving element 600 according to the first embodiment. Thus, the light receiving element 2100 can also be adapted to detect signal light having a lower intensity without increasing the PD length. In addition, the light receiving element 2100 can also supply a detection signal having a sufficient signal level to a subsequent electronic circuit at a high frequency.

As a specific example of the structure of the light receiving element 2100 according to the fourth embodiment, as in the case of the light receiving element 1900 according to the third embodiment, the light receiving element described above as the light receiving element according to the first embodiment can be used. 600 configuration of a specific instance of the structure. However, for example, an InP layer having a thickness of 0.1 μm is formed as the buffer layer 2115 . In addition, the laminated member composed of the core 2112 and the buffer layer 2115 is formed to have a thickness greater than that of the n-type semiconductor layer 2102 .

For the manufacturing method of the light receiving element 2100, as in the case of the light receiving element 1900 according to the third embodiment, the method described above as the manufacturing method of the light receiving element 600 can be used. However, after the removing step as shown in FIGS. 14A and 14B , and before the deposition step as shown in FIGS. 15A and 15B , a step of depositing an InP film with a thickness of 0.1 μm is added.

[5. Fifth Embodiment]

FIG. 22 shows an example of the configuration of a light receiving device 2200 according to the fifth embodiment.

An optical receiving device 2200 shown in FIG. 22 shows an example of an optical coherent receiver for demodulating a signal modulated in a quadrature phase shift keying (QPSK) method. From the viewpoint of miniaturization and assembly cost reduction, the light receiving device 2200 can be expected to be developed as a waveguide-integrated type light receiving device in which an optical hybrid waveguide converts phase-modulated signal light into intensity-modulated signal light), and a photodiode (PD) are integrated on the same substrate.

As shown in FIG. 22 , the light receiving device 2200 includes a photodetector unit 2201 , a connecting waveguide unit 2202 , an optical mixing waveguide unit 2203 and an input waveguide unit 2204 . The photodetector unit 2201 includes four photodiode (PD) devices 2205 to 2208 . The connection waveguide unit 2202 includes four connection waveguides 2209 to 2212 . The optical hybrid waveguide unit 2203 has two inputs and four outputs. The input waveguide unit 2203 includes two input waveguides 2214 and 2215 .

The two input waveguides 2214 and 2215 of the input waveguide unit 2204 are connected to the two inputs of the 90-degree optical hybrid waveguide unit 2213 . The four connection waveguides 2209 to 2212 of the photodetector unit 2201 are connected to the four outputs of the 90-degree optical hybrid waveguide unit 2213 . The four connection waveguides 2209 and 2212 are also connected to the PD devices 2205 to 2208 of the corresponding photodetector unit 2201 .

In the light receiving device 2200, in the part of the PD device 2205 and the connection waveguide 2209, the light receiving elements 600, The photodetector unit 601 , 1801 , 1901 or 2101 and the waveguide unit 611 , 1811 , 1911 or 2111 in any one of 1800 , 1900 and 2100 . The same applies to the rest of the PD device and the connecting waveguide, that is, the PD device 2206 and the connecting waveguide 2212 , the PD device 2207 and the connecting waveguide 2210 , and the PD device 2208 and the connecting waveguide 2211 . The optical mixing waveguide unit 2203 and the input waveguide unit 2204 have the same layered structure as the connection waveguide unit 2202 and are formed over the same substrate as the photodetector unit 2201 and the connection waveguide unit 2202 .

The operation of the light receiving device 2200 is described. The QPSK modulated signal light enters the input waveguide 2214, and the local oscillator (hereinafter referred to as LO) light enters the input waveguide 2215 as a reference light. The 90-degree optical hybrid waveguide unit 2213 receives the signal light and the LO light via the input waveguides 2214 and 2215, respectively. The 90-degree optical mixing waveguide unit 2213 demodulates the QPSK modulated signal light by causing interference between the LO light and the signal light, thereby generating I-channel signal light 180° out-of-phase with each other and Q-channel signal 180° out-of-phase with each other Light. The 90-degree optical hybrid waveguide unit 2213 outputs complementary I-channel signal light to connection waveguides 2209 and 2210 , and outputs complementary Q-channel signal light to connection waveguides 2211 and 2212 .

PD devices 2205 and 2206 receive complementary I-channel signal light from 90-degree optical hybrid waveguide unit 2213 via connection waveguides 2209 and 2210, respectively. Each of the PD devices 2205 and 2206 detects the received I-channel signal light as an electrical signal, and generates an I-channel signal (electrical signal). PD devices 2207 and 2208 receive complementary Q-channel signal light from 90-degree optical hybrid waveguide unit 2213 via connecting waveguides 2211 and 2212, respectively. Each of the PD devices 2207 and 2208 detects the received Q-channel signal light as an electrical signal, and generates a Q-channel signal (electrical signal).

As the 90-degree optical hybrid waveguide unit 2213 as described above, for example, a 4×4 multimode interference (hereinafter referred to as MMI) waveguide having four inputs and four outputs can be used. In this case, each of the input waveguides 2214 and 2215 is connected to two inputs of a 4x4 MMI waveguide. Connecting waveguides 2209 to 2212 are connected to the four outputs of the 4x4 MMI waveguides.

In the light receiving device 2200 according to the fifth embodiment, as in the cases of the receiving elements 600, 1800, 1900, and 2100 according to the first to fourth embodiments, in improving the light absorption efficiency in the photodetector unit 2201 At the same time, the I-channel signal and the Q-channel signal generated in the photodetector unit 2201 with a sufficient signal level can also be supplied at a high frequency to a subsequent electronic circuit.

The light receiving device 2200 can also perform an output operation suitable for high-intensity light input in which the intensity of input signal light is high. Therefore, for example, when the phase-modulated signal light is demodulated by converting the signal light into intensity-modulated signal light (complementary I-channel signal light and complementary Q-channel signal light) in the 90-degree optical hybrid waveguide unit 2213, Even if the intensity of the LO light is increased in order to increase the intensity of the converted signal light, in the PD devices 2205 to 2208, degradation of high-frequency characteristics of the input high-intensity signal light can be reduced.

In the four PD devices 2205 to 2208 included in the photodetector unit 2201, respective n-type semiconductor layers are formed independently. Thus, not only p-side electrodes but also n-side electrodes can be formed so as to be electrically isolated between the respective PD devices 2205 to 2208 to ensure sufficient electrical isolation between the respective PD devices 2205 to 2208 . Therefore, undesired crosstalk between the PD devices 2205 to 2208 can be reduced, thereby enabling the light receiving device 2200 to receive signal light with little error.

Although an optical coherent receiver is given as an example of the waveguide-integrated type light receiving device 2200 in the fifth embodiment described above, the fifth embodiment is not limited thereto. Any device in which a PD and a waveguide are integrated can be used, and the light receiving element 600 , 1800 , 1900 , or 2100 according to each of the first to fourth embodiments can be applied to such a device.

[6. Sixth Embodiment]

FIG. 23 shows an example of the configuration of a light receiving device 2300 according to the sixth embodiment.

An optical receiving device 2300 shown in FIG. 23 represents an example of an optical coherent receiver module for demodulating a modulated signal in a bipolar-quaternary phase-shift keying (DP-QPSK) method.

As shown in FIG. 23, the light receiving device 2300 includes optical coherent receivers 2301 and 2302, transimpedance amplifiers (trans-impedance amplifier) (hereinafter referred to as TIA) 2303 to 2306, polarization beam splitter (polarization light splitter) (hereinafter referred to as Herein referred to as PBS) 2307 and 2308, lenses 2309 to 2314, and mirrors 2315 and 2316. In addition, optical fiber cables 2317 and 2318 are connected to the light receiving module 2300 .

The light receiving module 2300 receives DP-QPSK modulated signal light via an optical fiber cable 2317 and receives LO light as reference light via an optical fiber cable 2318 . The signal light modulated by DP-QPSK includes two paths of signal light having different and mutually orthogonal polarization directions, and the two paths of signal light transmit different lights from each other.

The signal light modulated by DP-QPSK enters the PBS 2307 through the lens 2309, and is divided into two paths of signal light with different polarization directions by the PBS 2307. One of the split signal lights enters the optical coherent receiver 2301 through the lens 2311 , and the other enters the optical coherent receiver 2302 through the mirror 2315 and the lens 2313 . LO light is similarly supplied to each of optical coherent receivers 2301 and 2302 .

As each of optical coherent receivers 2301 and 2302, a light receiving device 2200 according to the fifth embodiment as shown in FIG. 22 can be used. Each of the optical coherent receivers 2301 and 2302 receives QPSK modulated signal light and LO light, and demodulates the QPSK modulated signal by causing interference between the LO light and the signal light.

The optical coherent receiver 2301 detects the complementary I-channel signal light obtained by demodulation as a complementary electric signal (I-channel signal). The optical coherent receiver 2301 detects the complementary Q-channel signal light obtained by demodulation as a complementary electric signal (Q-channel signal). The optical coherent receiver 2301 supplies a complementary I-channel signal (electrical signal) obtained by detection to the TIA 2303, and supplies a complementary Q-channel signal (electrical signal) obtained by detection to the TIA 2304. Similarly, optical coherent receiver 2302 supplies a complementary I-channel signal to TIA 2305 and a complementary Q-channel signal to TIA 2306.

Each of the TIAs 2303 to 2306 receives a complementary I-channel signal or a complementary Q-channel signal, and differentially amplifies the signal level.

In the light receiving module 2300 according to the sixth embodiment, as in the light receiving device 2200 according to the fifth embodiment, while improving the light absorption efficiency in the optical coherent receivers 2301 and 2302, it is also possible to use I-channel signals and Q-channel signals having sufficient signal levels are supplied to each of the TIAs 2303 to 2306 .

In addition, an output operation suitable for a high-intensity light input in which the intensity of input signal light is high may be performed in the light receiving module 2300 . Therefore, for example, when the phase modulated signal light is demodulated by converting the signal light into the intensity modulated signal light in each of the optical coherent receivers 2301 and 2302, even if the LO light is increased to increase the intensity of the converted signal light The intensity can also reduce the attenuation of the high-frequency characteristics of the input high-intensity signal light.

In the plurality of PD devices included in each of the optical coherent receivers 2301 and 2302, the corresponding n-type semiconductor layers are independently formed. Thus, not only p-side electrodes but also n-side electrodes may be formed to be electrically isolated between individual PD devices, thereby ensuring sufficient electrical isolation between individual PD devices. Accordingly, undesired crosstalk between a plurality of PD devices can be reduced, thereby enabling the light receiving module 2300 to receive signal light with little error.

The light receiving element, the light receiving device, and the light receiving module according to each exemplary embodiment have been described above. However, the embodiments are not limited to the embodiments specifically discussed herein, and various changes and modifications may be made to the embodiments without departing from the scope of the appended claims.

All examples and conditional language described herein are intended to be used for instructional purposes to help the reader understand the concepts of the invention and the inventor's improvements to the prior art, and should be construed as not limiting to these specifically enumerated examples and conditions, The composition of these examples in the specification is also not intended to demonstrate the advantages and disadvantages of the present invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions and alterations could be made hereto without departing from the spirit and scope of the invention.

Claims (6)

1. A light receiving element comprising: a core configured to propagate signal light; a first semiconductor layer having a first conductivity type configured to receive the signal light from the core along a first direction, the core extending in the first direction; an absorbing layer configured to absorb signal light received by the first semiconductor layer; and a second semiconductor layer having a second conductivity type opposite to the first conductivity type; wherein the upper surface of the core is farther from the substrate than the upper surface of the first semiconductor layer and is closer to the substrate than the upper surface of the absorber layer, the core and the first semiconductor layer are arranged in on or over the substrate. 2. The light receiving element according to claim 1, Wherein the thickness of the first semiconductor layer is not less than half of the thickness of the core. 3. A light receiving device, comprising: a waveguide unit disposed in the first region of the substrate, the waveguide unit including a plurality of waveguides configured to propagate multiple first lights; and a photodetector unit disposed in the second region of the substrate, the photodetector unit including a plurality of light receiving elements configured to receive the plurality of first lights from the plurality of waveguides, wherein each of the plurality of waveguides comprises: a core configured to propagate a corresponding one of the multiple first lights, and wherein each of the plurality of light receiving elements comprises: The first semiconductor layer has a first conductivity type, and the first semiconductor layer is configured to receive a corresponding one of the multiple first lights from a corresponding one of the plurality of cores along a first direction, so that said corresponding one core extends in said first direction, said core being thicker than half the thickness of said first semiconductor layer; an absorbing layer configured to absorb the corresponding path of first light received by the first semiconductor layer; and The second semiconductor layer has a second conductivity type opposite to the first conductivity type. 4. A light receiving device, comprising: a first waveguide unit disposed in the first region of the substrate, the first waveguide unit configured to propagate multiple paths of first light; a second waveguide unit disposed in the second region of the substrate, the second waveguide unit configured to receive the multiple paths of first light and generate multiple paths of second light based on the multiple paths of first light; a third waveguide unit disposed in a third region of the substrate, the third waveguide unit including a plurality of waveguides configured to propagate the multiple paths of second light; and a photodetector unit disposed in the fourth region of the substrate, the photodetector unit including a plurality of light receiving elements configured to receive the plurality of second lights from the plurality of waveguides, wherein each of the plurality of waveguides comprises: a core configured to propagate a corresponding one of the plurality of second lights, and wherein each of the plurality of light receiving elements comprises: The first semiconductor layer has a first conductivity type, and the first semiconductor layer is configured to receive a corresponding one of the plurality of second lights from a corresponding one of the plurality of cores along a first direction, so that said corresponding one core extends in said first direction, said core being thicker than half the thickness of said first semiconductor layer; an absorbing layer configured to absorb the corresponding path of second light received by the first semiconductor layer; and The second semiconductor layer has a second conductivity type opposite to the first conductivity type. 5. The light receiving device according to claim 4, wherein the multiple paths of first light include signal light and reference light; and the second waveguide unit includes a multimode interference waveguide configured to generate the signal light by causing interference between the signal light and the reference light. Said multi-channel second light. 6. A light receiving module, comprising: a plurality of light receiving devices configured to receive multiple first lights, the plurality of light receiving devices configured to detect the multiple first lights and output a plurality of electrical signals based on the multiple first lights; and a plurality of amplifiers configured to receive the plurality of electrical signals and amplify the plurality of electrical signals, Wherein each of said plurality of light receiving devices comprises: a first waveguide unit disposed in the first region of the substrate, the first waveguide unit configured to propagate the multiple paths of first light; a second waveguide unit disposed in the second region of the substrate, the second waveguide unit configured to receive the multiple paths of first light and generate multiple paths of second light based on the multiple paths of first light; a third waveguide unit disposed in a third region of the substrate, the third waveguide unit including a plurality of waveguides configured to propagate the multiple paths of second light; and a photodetector unit disposed in the fourth region of the substrate, the photodetector unit including a plurality of light receiving elements configured to receive the plurality of second lights from the plurality of waveguides, wherein each of the plurality of waveguides comprises: a core configured to propagate a corresponding one of the plurality of second lights; and wherein each of the plurality of light receiving elements comprises: A first semiconductor layer having a first conductivity type, the first semiconductor layer is configured to receive a corresponding one of the multiple paths of second light from a corresponding one of the plurality of cores along a first direction, the a corresponding one core extending in said first direction, said core being thicker than half the thickness of said first semiconductor layer; an absorbing layer configured to absorb the corresponding path of second light received by the first semiconductor layer; and The second semiconductor layer has a second conductivity type opposite to the first conductivity type.